Telephone-transmitter.



No. 644,205. Patented Feb. 27, I900. A; K. KELLER;

(Application filed Aug. 20, 1898.)

(No Modal m: NORBXE PUERS co momuywou wqSHINGTQrL u. c.

- UNITED STATES PATENT Eric.

ALBERT K. KELLER, OF PHILADELPHIA, PENNSYLVANIA.

.TELEPHONE-T'RANMITTER.'

SPECIFICATION forming part of Letters Patent No. 644,205, dated February 2'7, 1906.

Application filed August 20, 1898. Serial No. 689,117. (No modell) T0 ctZZ whom it may concern:

Be it known that I, ALBERT K. KELLER, a citizen of the United States, residing in the city and county of Philadelphia, in the State of Pennsylvania, have invented a certain new and useful Improvementin Telephone-Transmitters, of which the following is a specification.

My invention relates to telephone-transmitters of the class commonly known as granular transmitters'i. e. those in which atmospheric vibrations due to speech are caused to change the relation or pressure existing between the constituent particles of a finely-divided mass of carbon in order to alter its resistance,andthereby propagate current-waves corresponding to the atmospheric disturbances. Many forms of such transmitters are in use, but with few exceptions they are liable to derangements of several kinds; and it is the object of this invention to avoid these derangements, or at least reduce the liability thereto to a minimum, and at the same time produce an instrument which is simple and comparatively inexpensive to construct.

'The principal troubles heretofore experienced with granular carbon transmitters have been the liability of the carbon granules to pack after continued use, the liability of parts upon which the accurate working depends to get out of adjustment, the difficulty of readjustment,the oversensitiveness to loud sounds when adjusted finely, and the lack of sensitiveness if otherwise adjusted. I have succeeded in avoiding to a great extent all of these troubles by the construction herein described.

The principal features of the instrument are a solid shell in two parts accurately centered and self-centering whenever put together and coacting electrodes, one of which works as a plunger or piston, the electrodes being carried upon and centered by the two parts of the shell, respectively.

Various details of construction will be pointed out in the description.

My invention is fully illustrated in the accompanying drawings, wherein the same letters of reference indicate the same parts throughout.

In the drawings, Figure 1 is a transvers sectional View of the transmitter assembled,

showing a portion of the supporting-arm, but omitting the mouthpiece. Fig. 2 is a face View of the rearhalf of the shell, showing the rear electrode. Fig. 3 is an inside view of the front half of the shell with the diaphragm and piston-electrode carried thereby. Fig. 4 is a rear view of the shell removed from the supporting-arm. Fig. 5 is a face View of the instrument with the mouthpiece removed; and Fig. 6 is a detail View, on a larger scale, of the plunger-electrode.

In the drawings, A is the shell or inclosing casing of the transmitter, made in two parts a and (1. These parts are accurately turned and centered in a machine, both being solid castings of sufficient thickness to prevent the easy transmission of soundvibrations through their substance. The front half a fits accurately within the rear half, forming a smooth and tight joint 0?. Accurately contered with regard to the shell and having its walls integral with the part a is a chamber a of cylindrical form. This chamber is provided with a rear wall or web a also integral with the bodyof the part a and provided with a central screw-threaded perforation. The walls of the chamber extend rearwardly a sufficient distance to form a cup or a depression a and are internally screw-threaded to fit corresponding threads upon the supporting arm a, as shown.

B and B represent the two electrodes, the former of which is attached to and solidly supported by the rear part of the shell a within the chamber a and the latter is carried upon and moved by a spindle I), attached to the diaphragm D. The electrode B is supported within a cup b, within which it is retained by the side flange of the cup being spun over upon it. b working in the threaded perforation of the rear wall a of the chamber a and provided upon the rear face of said wall with a lock-nut 5 adapted to retain the screw, and thereby the electrode, in position after adjustment. The front or vibrating electrode B is secured within a metallic cup 12 having its edges spun over upon the electrode, as in the case of the electrode B. The cup b is carried by the spindle b, which is externally screw-threaded throughout its whole length and is tapped for the reception of a round-headed screw 12 The The cup is carried. by a screw the pliable disk is the same as the inner di-.

ameter of the chamber a within which it works. The washer b is secured to the electrode B by means of a threaded metallic washer 19 which after the disk 12 has been slipped upon the screw-threaded spindle is screwed thereon and clamps the disk b tightly against the cup I), as shown.

The front half a of the shellAis provided with a shoulder or bead a and another flange a the latter fitting snugly within the rear half a of the shell and the former abutting thereagainst. The flange a is provided internally with screw-threads adapted to be engaged by corresponding threads upon the periphery of a clamping-ring O. This ring 0 serves, as shown in Fig. 1, to firmly secure the diaphragm D upon the inner face of the front half a of the shell. In order to lessen the friction of the ring upon the diaphragm in adjusting it, I provide a friction-ring C, which is not screw-threaded, but lies loosely upon and around the periphery of the diaphragm untilthe ring 0 is screwed home. In assembling the instrument a rubber band is stretched over and around the edge of the diaphragm in a manner well understood in the art, which serves at once to insulate the diaphragm from the shell and to enable the clamping-ring to fit smoothly and evenly all around with an equal pressure, thus avoiding lines of stress in the diaphragm which would tend to interfere with its freedom of vibration. At its central point the diaphragm is provided with a perforation just large enough to admit the screw b The operation of assembling the parts thus described is exceedingly simple and infallibly reliable in its results. The rear half of the shell a (shown in Figs. 1, 2, and 4) is first taken in hand and the rear electrode B is seated against the wall a by screwing its stem b through the perforation therein. The lock-nut b is then applied from the rear. Then taking up the front half of the shell a the diaphragm D is laid upon the inner face thereof, the friction-ring O placed thereon, and the clamping-ring O screwed down tightly by means of a spanner working in the holes 0. (Shown in Fig. 3.) The diaphragm is thus rigidly attached to and to all intents and purposes forms an immovable part of the shell A. The stem 17 of the front electrode B is then held alined with the central hole in the diaphragm and the round-headed screw I) is inserted therein and screwed tightly into the spindle or stem 1) by means of another spanner working in the holes 2) in the head of the suitable mouthpiece.

screw. The front electrode is thus rigidly at tached to the diaphragm and with it forms an immovable part of the front half a of the shell A. I prefer to use the spanners with these parts rather than ordinary actuating means in order to render it difficult for persons unprovided therewith to tamper with the instrument. It must now be apparent that with the parts thus assembled it only remains to put the two halves a and a (shown separated in Figs. 2 and 3) together to bring the entire instrument into perfect working condition. The two halves of the shell are alined or centered once for all in the beginning. Each carries an electrode immovably secured and perfectly centered, and therefore it follows that when put together the electrodes themselves must always and inevitably bein alinement.

It will be observed that as the front electrode is carried entirely by the diaphragm it does not depend for its support in the slightest degree upon the walls of the chamber u nor upon the engagement of the washer b therewith. The sole function of the latter is to prevent the escape of the granular carbon g. It should be observed here that the chamber 61, 18 lined with paper or. its walls are coatedwith shellac in order to prevent short-circuiting therethrough.

I do not wish to limit myself to the means I have shown for securing the rear electrode B, as instead of the screw-threaded stem 11 engaging with threads in the wall a the orifice in said wall may be plain and the nut b serve to hold the electrode and its containing-cup firmly against the rear wall of the chamber.

When the instrument, having been assembled, is screwed upon the supporting arm A, as shown in Fig. 1, the stem 19 and the nut b are completely inclosed and protected.

, It will be understood that the front half a of the shell is provided with a suitable orifice a, screw-threaded at a, for the reception of a The rear half a of the shell is provided with a rubber-hushed orifice a for the passage of a conducting-wire a, connected to the diaphragm, and thus conveying current to the front electrode. The circuit is completed through the shell from the rear electrode, or two wires may be provided.

Having thus described my invention, what I claim, and desire to secure by Letters Patent, is V 1. In a telephone-transmitter a containingshell divided into two parts accurately centered so that when fitted together their axes are coincident, a central chamber formed in the body of the rear part, an electrode seated in said chamber, a diaphragm carried upon the face of the front part, a 1ocking-ring over the diaphragm clamping it around its edges to said front part, and a plunger-electrode carried on the diaphragm and centered there by, substantially as described.

2 in a telephonetransmitter a plungerelectrode comprising a spindle or stem, a cuphead thereon, a carbon button seated rigidly in said cup, a pliable disk washer of greater diameter than the cup, two stiff disks, one on either side thereof, and a clamping-nut on the stem holding the three disks firmly against the head, substantially as described.

3. In a telephone-transmitter a metallic shell divided into two parts, accurately centered so that when fitted together their axes are coincident, a cylindrical chamber centrally formed directly in and having its walls integral with the body ofthe rear part of the shell, said chamber being coated inside with insulating material, an electrode fixed rigidly within said chamber, a diaphragm carried by and rigidly clamped around its edges to the front part of the shell, asecond electrode cen trally mounted on the diaphragm, of a diameter somewhat less than that of the chamber, a pliable Washer extending around the periphery of said second electrode, granular carbon within the chamber, and suitable circuit connections, the Whole being so arranged that when the parts of the shell are placed. 

